Process for preparing alkylthiobenzimidazoles

ABSTRACT

The invention concerns a new process for the preparation of biologically active 2-[(alkoxycarbonyl)amino]-5-(alkylthio)-1H-benzimidazoles of the general formula (V) ##STR1## wherein R and R 1  independently stand for alkyl having 1 to 3 carbon atoms.

The present invention relates to a new process for the preparation ofalkylthiobenz-imidazoles. More particularly, this invention concerns anew process for preparing biologically active2-[(alkoxycarbonyl)amino]-5-(alkylthio)-1H-benzimidazoles of the formula(V) ##STR2## wherein

R and R¹ independently stand for alkyl having 1 to 3 carbon atoms.

The compounds of the formula (V) are conventionally prepared from thecorresponding 4-alkylthio-phenylenediamines by reactants capable offorming an imidazole ring. Suitable reactants include the correspondingcarboalkoxycyane amides, directly yielding the desired end products, andbromocyane, which results in the formation of a2-amino-5-alkylthiobenzimidazole, which is then reacted with an alkylchloroformate to give the desired end product. A detailed description ofthese processes is be found in the U.S. Pat. No. 3,956,499 and in theHungarian Pat. No. 172,538. These patents disclose the preparation of2-[(methoxycarbonyl)amino]-5-(propylthio)-1H-benzimidazole, a prominentrepresentative of the compounds of the formula (V), having valuableanthelmintic properties.

The most important disadvantages of the processes known in the artconsist in the fact that 4-alkylthio-1,2-phenylenediamines are ratherexpensive and difficult to prepare, some of the reactants employed aretoxic and have an unpleasant odor, and a dangerous and expensivecatalytic hydrogenation step is involved.

The present invention relates to a new process for the preparation of2-[(alkoxycarbonyl)amino]-5-(alkylthio)-1H-benzimidazoles of the formula(V)--wherein R and R¹ are as hereinbefore defined--which is devoid ofthe above disadvantages. According to the invention compounds of theformula (V) are prepared by reacting (1H-benzimidazol-2-yl)carbamic acidalkyl esters of the formula (I) ##STR3## wherein R has the same meaningas defined above, with

(a) chlorosulfonic acid, or

(b) oleum, to yield a corresponding2-[(alkoxycarbonyl)amino]-1H-benzimidazole-5-sulfonic acid of theformula (II) ##STR4## wherein R is as defined above, and subsequentlywith a chlorinating agent,

reducing a 2-[(alkoxycarbonyl)amino]-1H-benzimidazole-5-sulfonic acidchloride of the formula (III) ##STR5## where R is as defined above,

obtained, by variant (a) or (b) and finally reacting a2-[(alkoxycarbonyl)amino]-1H-benzimidazole-5-thiol of the formula (IV)##STR6## wherein R is as defined above, obtained with an alkyl halide ofthe formula

    R.sup.1 --Hal                                              (VI)

wherein R¹ is as hereinbefore defined and Hal represents halogen.

The term "alkyl" alone or in alkyl-containing groups is used to refer tostraight or branched chained hydrocarbon groups having 1 to 3 carbonatoms, i.e. methyl, ethyl, n- and isopropyl groups.

The term "halogen" stands for fluorine, chlorine, bromine or iodine.

As chlorinating agents phosphorus oxychloride, phosphorus pentachlorideor pyrocatechyl phosphorus trichloride can for example be used.

The reduction of the compounds of the formula (III) is preferablycarried out in an aqueous acidic medium, with metals or metal salts.

2-[(alkoxycarbonyl)amino]-1H-benzimidazole-5-sulfonic acids of theformula (II) and salts thereof,

2-[(alkoxycarbonyl)amino]-1H-benzimidazole-5-sulfonic acid chlorides ofthe formula (III) and salts thereof, and

2-[(alkoxycarbonyl)amino]-1H-benzimidazole-5-thiols of the formula (IV)and salts thereof, obtained as intermediates in the synthesis accordingto the invention are new compounds.

2-[(Alkoxycarbonyl)amino]-1H-benzimidazole-5-sulfonic acids of theformula (II) are obtained in the form of white crystals, by reacting acorresponding (1H-benzimidazol-2-yl)-carbamic acid alkyl ester of theformula (I) with a 20% oleum at 30° to 60° C. and pouring the reactionmixture into ether.

2-[(Alkoxycarbonyl)amino]-1H-benzimidazole-5-sulfonic acid chlorides ofthe formula (III) can be prepared by

(a) reacting a corresponding compound of the formula (I) withchlorosulfonic acid at a temperature between 15° C. and 40° C. andsubsequently pouring the reaction mixture into absolute alcohol or onice, when the product is obtained as a hydrochloride, or into a mixtureof ether and ethyl acetate, when a corresponding sulfuric acid additionsalt is obtained, or

(b) converting a compound of the formula (II) into the sodium saltthereof with sodium hydroxide in a methanolic medium, melting the saltobtained with phosphorus pentachloride at 110° C. and finally pouringthe reaction mixture on ice.

When a 2-[(alkoxycarbonyl)amino]-1H-benzimidazole-5-sulfonic acidchloride of the formula (III) is reduced with a metal or metal salt inan aqueous acidic medium, at 0° to 100° C.,2-[(alkoxycarbonyl)amino]-1H-benzimidazole-5-thiol of the formula (IV)is obtained, which precipitates as a white crystalline substance.

The compound of the formula (IV) obtained is then dissolved in dimethylformamide, the pH is adjusted to 8 to 9 with an aqueous alkalinesolution, it is reacted with an alkyl halide, preferably bromide at roomtemperature and the solution is diluted with water to yield2-[(alkoxycarbonyl)amino]-5-alkylthio-1H-benzimidazole of the formula(V), which can easily be filtered off.

An important advantage of the process according to the invention overthe methods known in the art consists in the fact that compounds of thegeneral formula (I) used as starting materials are cheap industrialproducts, from which end products of the formula (V) can be prepared bysimple technological steps, using readily available and cheap reactants.

Further details of the invention are to be found in the followingExamples, which are not intended to limit the scope of the invention inany way.

EXAMPLE 1

2-[(Methoxycarbonyl)amino]-1H-benzimidazole-5-sulfonic acid

Into a 250-ml. four-neck, round-bottomed flask, equipped with a stirrer,thermometer and a sulfuric acid bubbler 120 ml. of a 20% oleum areweighed, whereupon 38.4 g. (0.2 moles) of(1H-benzimidazol-2-yl)-carbamic acid methyl ester are added dropwise, at30° to 40° C., under a slight cooling with ice water, in 15 to 20minutes. The temperature is then raised to 55° to 60° C. and thereaction mixture is stirred for two hours.

1200 ml. of ethyl ether are cooled to -10° C. with salted ice and theabove reaction mixture is poured into the cool ether, at a rate, whichensures that the temperature does not exceed 0° C.

The title product precipitates as a white, crystalline substance, whichis then filtered off, washed with cooled ether and subsequently with 100ml. of cooled absolute ethanol and dried. Weight: 43.5 g. (theoretical:54.26 g.). Yield: 80%

Analysis:

found: C=39.2%, H=3.5%, N=15.1%, S=12.1% calculated: C=39.84%, H=3.34%,N=15.49%, S=11.8%

EXAMPLE 2 2-[(Methoxycarbonyl)amino]-1H-benzimidazole-5-sulfonic acidchloride. HCl

Into a 500-ml. flask, equipped with a stirrer 81.3 g. (0.3 moles) of2-[(methoxycarbonyl)amino]-1H-benzimidazole-5-sulfonic acid and 300 ml.of methanol are weighed. The pH of the reaction mixture is adjusted to7.5 with dropwise addition of a 40% aqueous sodium hydroxide solution atroom temperature. The starting compound is dissolved in the mixturewhereupon precipitation of2-[(methoxycrbonyl)amino]-1H-benzimidazole-5-sulfonic acid sodium saltcan be observed. After stirring for one hour, the mixture is filtered,and the precipitate is washed with a small portion of methanol and issubsequently dried. Weight: 90 g.

The dry sulfonic acid salt is then melted with 130 g. (0.625 moles) ofphosphorus pentachloride at 110° C. and is stirred at the sametemperature for an additional two hours.

The mixture is poured onto 400 g. of broken ice, is washed with icewater and subsequently with 100 ml. of absolute ethanol of -10° C., andis dried. 82 g. of the title compound are obtained (theoretical: 97.86g.).

Yield: 84%

Analysis:

found: C=32.9%, H=3.0%, Cl=21.6%, N=13.0%, S=9.75%. calculated:C=33.14%, H=2.78%, Cl=21.74%, N=12.88%, S=9.83%.

EXAMPLE 3

2-[(Methoxycarbonyl)amino]-1H-benzimidazole-5-sulfonic acid chloride.HCl

Into a 250-ml. four-necked, round-bottomed flask, equipped with astirrer, thermometer and a sulfuric acid bubbler 100 ml. (178.7 g, 1.53moles) of chlorosulfonic acid are weighed, followed by the addition of38.4 g. (0.2 moles) of (1H-benzimidazol-2-yl)-carbamic acid methyl esterat 15° to 20° C., under slight cooling with ice water, in about 30minutes. The reaction mixture is then heated up to 40° C. and is stirredat this temperature for 2.5 hours. The reaction mixture is poured into1000 ml. of absolute ethanol, and cooled to -10° C. at a rate, whichensures that the temperature does not exceed 0° C. An intensive coolingwith salted ice is required.

The precipitated white crystalline product is filtered off, washed with100 ml. of cooled absolute ethanol and dried. Weight: 60.6 g.(theoretical: 62.2 g.).

Yield: 93%.

Melting point: 250° C.

Analysis:

found: C=32.94%, H=3.02%, Cl=21.64%, N=12.91%, S=9.81%. calculated:C=33.14%, H=2.78%, Cl=21.74%, N=12.88%, S=9.83%.

EXAMPLE 4 2-[(Methoxycarbonyl)amino]-1H-benzimidazole-5-sulfonic acidchloride. HCl

The procedure described in Example 3 is followed, except that theproduct is isolated from the reaction mixture as follows:

The reaction mixture containing chlorosulfonic acid is poured onto 800g. of broken ice. The precipitated product is filtered off, washed witha small portion of ice water and subsequently with 100 ml. of absoluteethanol cooled to -10° C., and is dried. 52.1 g. of the title compoundare obtained (theoretical: 65.2 g.).

Yield: 80%

The acid chloride isolated from water is preferably used without drying,since during drying decomposition takes place.

EXAMPLE 5 2-[(Methoxycarbonyl)amino]-1H-benzimidazole-5-sulfonic acidchloride.H₂ SO₄

Into a 200-ml. four-necked, round-bottomed flask, equipped with astirred, thermometer and a sulfuric acid bubbler 100 ml. (175.7 g.; 1.53moles) of chlorosulfonic acid are weighed, followed by the addition of38.4 g. (0.2 moles) of (1H-benzimidazol-2-yl)-carbamic acid methyl esterat 15° to 20° C., under slight cooling with ice water, in about 30minutes. The reaction mixture is heated up to 40° C., is stirred at thistemperature for 2.5 hours, whereupon it is poured into a mixture of 1000ml. of ethyl ether and 300 ml. of ethyl acetate cooled to -10° C. at arate, which ensures that the temperature does not exceed 0° C.

The precipitated white crystalline product is filtered off, washed with200 ml. of cooled ether and dried in a vacuum desiccator. (The driedproduct is not hygroscopic any more.) 64.40 g. of the title compound areobtained (theoretical: 77.4 g.).

Yield: 83.2%, melting point: 142° to 145° C. (decomp.)

Analysis:

found: C=27.52%, H=2.8%, Cl=9.18%, N=10.12%, S=16.45%, calculated:C=27.87%, H=2.6%, Cl=9.14%, N=10.83%, S=16.54%.

EXAMPLE 6 2-[(Methoxycarbonyl)amino]-5-propylthio-1H-benzimidazole

Into 110 ml. of a 40% aqueous sulfuric acid solution 20 g. of Zn powderare added at 0° C., followed by the addition of 10.8 g. (0.033 moles) of2-(methoxycarbonyl)amino-1H-benzimidazole-5-sulfonic acid chloridehydrochloride. The reaction mixture is then stirred at 0° C. for twohours. Thereafter it is heated up to 80° to 90° C. and stirred at thistemperature for one hour.2-[(Methoxycarbonyl)amino]-1H-benzimidazole-5-thiol precipitates as awhite crystalline substance. It is cooled to room temperature, filteredoff and washed with a small portion of ice water. The precipitate isdissolved in a five-times amount of dimethyl formamide related to itsweight. The undissolved zinc is filtered off and washed with dimethylformamide. The pH of the reaction mixture is adjusted to 8 to 9 with a40% aqueous sodium hydroxide solution, 6 ml. of n-propyl bromide areadded, while the temperature is kept at 25° to 30° C. by cooling withice water. The mixture is stirred for half an hour and is subsequentlyallowed to stand for 48 hours. The precipitate is filtered off, washedwith water and then with acetone, and is dried. 5.50 g. (62.8% oftheoretical) of the title compound are obtained, melting at 208° to 210°C. after recrystallization from chloroform (decomp.).

Analysis:

found: C=54.36%, H=5.64%, H=16.00%, S=11.92%. calculated: C=54.32%,H=5.70%, H=15.84%, S=12.00%.

EXAMPLE 7 2-[(Methoxycarbonyl)amino]-5-propylthio-1H-benzimidazole 10.8g. (0.033 moles) of2-[(Methoxycarbonyl)amino]-1H-benzimidazole-5-sulfonic acid chloridehydrochloride are suspended in 35 ml. of water, 33 g. of SnCl₂ are addedand the mixture is stirred at 50 C. for 30 minutes. A clear solution isobtained and then the precipitation of a crystalline substance can beobserved. The mixture is cooled to room temperature, filtered and theprecipitate is washed with a small portion of ice water.2-[(Methoxycarbonyl)amino]-1H-benzimidazole-5-thiol obtained is furthertreated as described in Example 6 to yield 5 g. of the title compound,melting at 210° C. EXAMPLE 82-[(Ethoxycarbonyl)amino]-1H-benzimidazole-5-sulfonic acid chloride. HCl

Into 100 ml. (178.7 g.; 1.53 moles) of chlorosulfonic acid 41 g. (0.2moles) of 1H-benzimidazol-2-yl)-carbamic acid ethyl ester are added at15° to 20° C. in about 30 minutes. The reaction mixture is heated up to40° C. and is stirred for 2.5 hours. It is then poured into absoluteethanol cooled to -10° C. The precipitated white crystalline product isfiltered off, washed with ethanol and dried. 59 g. of the title compoundare obtained (theoretical: 68 g.).

Analysis:

found: C=35.0%, H=3.1%, Cl=20.60%, N=12.70%, S=9.3%, calculated:C=35.3%, H=3.26%, Cl=20.84%, N=12.35%, S=9.43%.

EXAMPLE 9 2-[(Ethoxycarbonyl)amino]-5-ethylthio-1H-benzimidazole

Into 110 ml. of a 40% aqueous sulfuric acid solution 20 g. of zincpowder are added at 0° C. followed by the addition of 11.2 g. (0.033moles) of 2-[(ethoxycarbonyl)amino]-1H-benzimidazole-5-sulfonic acidchloride hydrochloride with stirring. The reaction mixture is stirred at0° C. for two hours. It is then heated up to 80° to 90° C. and isstirred at this temperature for one hour.2-[(Ethoxycarbonyl)amino]-1H-benzimidazole-5-thiol precipitates as awhite crystalline substance. The precipitate is dissolved in five-timesof its weight of dimethyl formamide and the undissolved zinc powder isfiltered off. The pH of the reaction mixture is adjusted to 8 to 9 withan aqueous sodium hydroxide solution, 5 ml. of ethyl bromide are addedand the mixture is allowed to stand for 48 hours. The title compoundprecipitates upon dilution with water. It is then filtered off andwashed with water and acetone. Weight: 4.4 g.

Analysis:

found: C=54.2%, H=5.58%, N=15.90%, S=11.85%; calculated: C=54.32%,H=5.70%, N=15.84%, S=12.08%.

EXAMPLE 10

2-[(Methoxycarbonyl)amino]-5-propylthio-1H-benzimidazole

Into 100 ml. of a 10% aqueous hydrochloric acid solution 1.5 g. of Snpowder are added at 0° to 10° C., followed by the addition of 10.8 g.(0.033 moles) of 2-[(methoxycarbonyl)amino]-1H-benzimidazol-5-sulfonicacid chloride hydrochloride. The reaction mixture is stirred at the sametemperature for one hour. Thereafter 10 g. of Fe powder are added and itis stirred at 25° to 30° C. for 6 hours. The metals are dissolved and2-[(methoxycarbonyl)amino]-1H-benzimidazole-5-thiol precipitates. Theprecipitate is filtered off, dissolved in a 10% aqueous potassiumhydroxide solution and is subsequently reacted with 6 ml. of n-propylbromide at 40° to 45° C.

The precipitated title compound is filtered off, washed with water andacetone, and dried. Weight: 4 g. Melting point: 213° to 214° C.(decomp.)

EXAMPLE 11 2-[(Methoxycarbonyl)amino]-5-propylthio-1H-benzimidazole

Into 100 ml. of a 10% aqueous hydrochloric acid solution 10.8 g. (0.033moles) of 2-[(methoxycarbonyl)amino]-1H-benzimidazole-5-sulfonic acidchloride hydrochloride and 10 g. of Fe powder are added at roomtemperature. The mixture is stirred at 70° to 80° C. for 5 hours,whereupon the precipitated2-[(methoxycarbonyl)amino]-1H-benzimidazole-5-thiol is filtered off andconverted into 2-[(methoxycarbonyl)amino]-5-propylthio-1H-benzimidazoleas described in Example 10. The product melts at 208° to 210° C.

EXAMPLES 12

2-[(Methoxycarbonyl)amino]-1H-benzimidazole-5-thiol

Into 100 ml. of a 10% aqueous hydrochloric acid solution 6 g. of Snpowder and 10.8 g. (0.033 moles) of2-[(methoxycarbonyl)amino]-1H-benzimidazole-5-sulfonic acid chloridehydrochloride are added at a temperature between 0° C. and 10° C. Thereaction mixture is stirred below 10° C. for two hours and subsequentlyat 25° C. for 10 hours. The starting compound is dissolved andthereafter the title compound precipitates. Weight: 6 g. (81.5%).Melting point: 214° to 215° C. (decomp.)

Analysis:

found: C=48.22%, H=4.20%, N=18.52%, S=13.80%, calculated: C=48.60%,H=4.06%, N=18.88%, S=14.39%.

We claim:
 1. A process for the preparation of a compound of the formula(V) ##STR7## wherein R and R¹ are each independently C₁ to C₃ alkyl,which comprises the steps of:(a) sulfonating a compound of the formula(I) ##STR8## with oleum at 30° to 60° C. to form a compound of theformula (II) ##STR9## (b) converting the compound of the formula (II)into the sodium salt thereof with aqueous sodium hydroxide; (c)chlorinating the sodium salt of the formula (II) with a chlorinatingagent selected from the group consisting of phosphorus oxychloride,phosphorus pentachloride, and pyrocatechyl phosphorus trichloride toform a compound of the formula (III) ##STR10## (d) reducing the compoundof the formula (III) at a temperature between 0° and 100° C. with ametal or metal salt in an aqueous acidic medium to form a compound ofthe formula (IV) ##STR11## and, (e) alkylating the compound of theformula (IV) with an alkyl halide of the formula (VI)

    R.sup.1 --Hal

wherein Hal is halogen at room temperature to yield the desired product.2. A process for the preparation of a compound of the formula (III)##STR12## wherein R is C₁ to C₃ alkyl, which comprises the steps ofchlorosulfonating a compound of the formula (I) ##STR13## withchlorosulfonic acid at a temperature between 15° and 40° C.
 3. A processfor the preparation of a compound of the formula (V) ##STR14## wherein Rand R¹ are each independently C₁ to C₃ alkyl, which comprises the stepsof:(a) chlorosulfonating a compound of the formula (I) ##STR15## withchlorosulfonic acid at a temperature between 15° and 40° C. to form acompound of the formula (III) ##STR16## (b) reducing the compound of theformula (III) at a temperature between 0° and 100° C. with a metal ormetal salt in an aqueous acidic medium to form a compound of the formula(IV) ##STR17## and, (c) alkylating the compound of the formula (IV) withan alkyl halide of the formula (VI)

    R.sup.1 --Hal

wherein Hal is halogen at room temperature to yield the desired product.4. A compund of the formula (II) ##STR18## wherein R stands for an alkylgroup having 1 to 3 carbon atoms, and salts thereof.
 5. A compound ofthe formula (III) ##STR19## wherein R stands for an alkyl group having 1to 3 carbon atoms, and acid addition salts thereof.
 6. A process for thepreparation of a compound of the formula (III) ##STR20## wherein R is C₁to C₃ alkyl, which comprises the steps of (a) sulfonating a compound ofthe formula (I) ##STR21## with oleum at 30° to 60° C. to form a compoundof the formula (II) ##STR22## (b) converting the compound of the formula(II) into the sodium salt thereof with aqueous sodium hydroxide; and(c)chlorinating the sodium salt of the compound of the formula (II) with acompound selected from the group consisting of phosphorus oxychloride,phosphorus pentachloride and pyrocatechyl phosphorustrichloride to yieldthe desired product.